Electronic valves and grid structures therefor



Feb. 2, 1965 F. H. REYNOLDS 3,168,571

ELECTRONIC VALVES AND GRID STRUCTURES THEREFOR Filed Jan. 12. 1961 4 Sheets-Sheet 1 8 5 mvsuurwa/ F Y /ij CONDUCT/N6 I W ca/voucr/lva Q INVENTQR Tmaoemcx H. R y 5 ATTORNEY Feb. 2, 1965 H. REYNOLDS 3,163,671

ELECTRONIC vALvEs AND GRID STRUCTURES THEREFOR Filed Jan. 12, 1961 4 Sheets-Sheet s INVENTOR Freepsmcx H v Re ue; a s

ELECTRONIC VALVES AND GRID STRUCTURES THEREFOR Filed Jan. 12. 1961 Feb. 2, 1965 F. H.-REYNOLD$ 4 Sheets-Sheet 4 CONDUC 7' [N6 INSUL A TIA/6 Invsw-rok FREDERICK H. Warm-" AT-rcaNEY 3,168,671 Patented Feb. 2 1965 United States Patent Ofi ice 3,163,671 ELEtITRQNlC VALVES AND GED STRUQTURES THERETEQR Frederick Harold Reynolds, Kenton, Harrow, England, assignor to rat- Magestys Postmaster General, London, England Filed lien. 12, 196i, 592- Ne. 82,284 Claims priority, application Great Britain, inn. ltd, 1960, 1,d39/6tl 12 Claims. (Cl. 313-350) This invention relates to electronic valves, and more particularly to grid structures for such valves and methods of manufacture of such grid structures.

In a thermionic valve, in order to achieve a high value of mutual conductance, the spacing between the control grid helix and the cathode may be reduced, together with reduction of the diameter of the wire used in winding the control grid helix. A known construction of control grid permitting the use of wire of the order of microns diameter for the control grid helix includes a rigid frame comprising spaced parallel rods, on which the grid helix is wound under tension, and end members which hold the rods rigidly in position. This construction commonly is known as a frame grid The screen grid operating voltage of a tetrode or pentode valve may be reduced by decreasing the spacing between the screen and control grids, together with reduction in the diameter of wire used in winding the screen grid helix. Here again the frame grid construction may be usefully employed.

In order to obtain a valve having a high mutual conductance and low screen grid operating voltage and there fore requiring a low plate supply voltage, both cathodecontrol grid and control grid-screen grid spacings must be reduced. If these grids are of frame grid construction and the control grid is inserted within the screen grid, as is a normal method of assembly, then a limit on the spacing obtainable between these two grids or between the control grid and cathode is imposed by the necessary dimensions of the end members of the frame grid structures.

According to the present invention, a method of manufacturing a grid structure for an electronic valve includes the steps of providing a frame comprising. two inner control grid support rods rigidly maintained in spaced parallel relationship with each other, winding a control grid helix around the, said inner rods and under a tension sufiicient to maintain the helix in position on the inner rods, supporting two screen grid support rods in spaced parallel relationship with each other on theframe and in insulating relationship with the inner rods, the outer rods being positioned adjacent and outwardly of the respective inner rods, and winding a screen grid helix around the said outer rods to surround the control grid helix in spaced relationship therewith, the screen grid being wound under a tension suflicient to maintain the helix in position on the outer rods.

The control grid rods may be maintained in spaced parallel relationship by locating them between opposing pairs of rigid bracing members, or crossmembers, one pair at or toward either end of the rods, and fixedly securing respective rods of bracing members to each other so that the bracing members extend outwardly of the rods; the bracing members and control grid rods then form a rigid'frame. After winding the control grid helix on the portion of the frame defined between the cross-member pairs, the screen grid rods are located between the extending portions of the bracing members on respective sides of the rigid frame, and supported only by the frame in adjacent and insulating relationship with the control grid rods.

An electronic valve grid assembly manufactured in accordance with the invention comprises a rigid frame including a pair of inner rods rigidly maintained in spaced parallel relationship with each other, a control grid helix wound under tension around and secured to the inner rods, a pair of rods positioned outwardly of and adjacent the respective inner rods and in insulating relationship therewith, the outer rods being supported solely by the control grid frame, and a screen grid helix wound under tension around and secured to the outer rods and surrounding the control grid helix in spaced relationship therewith.

One form of such a grid structure comprises a frame including a pair of parallelspaced inner rodsand a pair of further rods located adjacent and outwardly of the inner rods and in insulating relationship therewith. The inner and outer rods are located between respective pairs of cross-members arranged one pair at or towards the either ends of the rods. The cross-members, or bracing members, are rigidly secured to the inner rods and also co-operate with the outer rods to maintain the latter in position on the frame. The control grid is wound under tension around, and secured to, the portion of the inner,

rods defined between the two pairs of cross-members and the screen grid overlies the control grid in spaced relationship therewith. The inner rods may be cylindrical and the outer rods may also be cylindrical and of greater diameters that the inner rods at least over the portions of the rods around which the screen grid is wound. Conveniently the outer rods may have flats formed at either side thereof over a limited portion of the rods and arranged to co-operate with the cross-members to securely locate the outer rods in position on the frame. In this construction the inner rods and cross-members may conveniently be made of molybdenum and brazed together whilst the outer rods may be made of a refractory insulating material.

In an alternative construction of a grid structure in accordance with the invention, the control grid rods and screen grid rods may each be made of a refractory insulating material and rigidly secured to metal end plates.

in a further construction in accordance with the inven tion the control grid rods and screen grid rods may each be made of metal and the ends of the rods held within insulating bush-es fixedly set in metal end plates. Conveniently the bushes may be made of synthetic ruby.

In the above constructions the metal components may be made of molybdenum but refractory insulating material conveniently may be synthetic sapphire which has a relatively high ultimate tensile strength and is capable of being precision worked, e.g. by grinding. Alternatively, polycrystallised alumina may be used and this material has the property of a more constant ultimate tensile strength/temperature relationship. The control grid and screen grid helices may each comprise tungsten wire.

A tetrode valve may be constructed which includes a grid structure in. accordance with the invention and such a valve may have a high mutual conductance and glow screen grid operating voltage. Such a valve has the advantage that it requires a relatively low plate supply voltage and further advantage that the dimensions of the valve can be reduced considerably as compared with a construction in which the control and screen helices are wound on separate frames and the control grid frame inserted within the screen grid frame. t

By way of example, a method of constructing a grid structure in accordance with the invention will now be described in greater detail as will various grid support. ing frameworks and atetrode valve including a grid structure in accordance with the invention. Reference will be made to the accompanying drawings in which:

Y n as? FIG. 1 is a front view of a novel grid structure,

FIG. 2 is a plan view of FIG. 1,

FIG. 3 is a front view of a tetrode valve electrode assembly,

a FIG. 4 is a side view of FIG. 3 and shown mounted within a glass envelope,

FIG. 5 is a view on the line A-A of FIG. 3,

FIG. 6 is a plan view of an alternative grid supporting frame,

FIG; 7 is a section on line BB of FIG. 6,

FIG. 8 is a plan view of another grid supporting frame, and

FIG. 9 is a section on line C-C of FIG. 8.

For the sake of clarity only portions of the control grid and screen grid helices have been shown in FIGS. 1, 3 and 4. In FIGS. 6-9 the grid helices are not illustrated.

The grid structure shown in FIGS. 1 and 2 is manufactured 'by spanning a pair of molybdenum rods 1 with pairs of cross-members 2, 3 also made of molybdenum, near the ends of rods 1. Individual cross-members 2 are arranged opposite to each other one on either side of rods 1 and cross-members 3 are similarly disposed but at the opposite ends of rods 1. The cross-member pairs 2, 3 maintain rods 1 in spaced parallel relationship and respective rods 1 and cross-members Z, 3 are brazed together, using an alloy consisting of 75% gold and 25% nickel, to form a rigid frame. As shown in the figures, cross-members 2, 3, extend outwardly beyond rods 1.

A control grid helix 4 is then wound under tension around rods, 1, the tension being sufiicient to maintain the wires of the helix in position on the rods. A suitable cementing powder is applied to the helix wires Where they overlie rods 1, this stage of assembly being carried out in known manner.

Cylindrical rods 5, of greater diameter than rods 1 and made of a refractory insulating material such as, for example, synthetic sapphire, are then located adjacent and outwardly of rods 1 between the extended regions of cross-members Z, 3 in such manner that flats 6.on rods 5 co-operate with cross-members 2, 3 to maintain the rods firmly in position. A screen grid helix 7 is thenwound under tension around rods 5, the tension again being sufiicient to maintainthe helix wires in position on those rods and to entrap a platinum tape 8 placed along the outside of one of rods 5 prior to the winding operation. Connections to the screen grid can then be made via tape 8.

The pitches of the screen and control grids may be different or equal as desired. in the latter case the helices may be so wound that the respective wires of the control and screen grids are in alignment.

cementing powder is applied to the screen grid helix in a manner similar to that used for the control-grid helix and the whole unit fired in order to vitrify the cementing powder. If so desired, one of the rods 5 may be slightly longitudinally displaced at this stage in order to incline the wires of the screen grid helix relative to the wires of the control grid helix.

It will be appreciated that the spacing between the control grid and screen grid will be dependent upon the difference between the radii of rods 1 and 5 (which can readily be manufactured to any desired value) and that the construction used will not limit the control gridcathode spacing.

A tetrode thermionic valve may be constructed using a grid structure as described above. Such a valve is shown 7 tending the length of tube 10. The filament is enclosed by a further tube 13 located within tube and which serves to insulate the filament from the latter tube. Tube 119 passes at either end through a correspondingly shaped central aperture in a cruciform shaped mica disc 14. Each mica disc 14 is sandwiched between two metal shield plates 14a which are supported from a disc in spaced relationship therewith. The shield plates have apertures through which various electrodes and leads, referred to below, can pass in spaced relationship with the shield plate. Tube 13 is located at its upper end by ceramic tubes 12 which surround the exposed ends of the filament and by a ceramic bush 15 which sup ports its lower end, the bush being held in position by a rod 16 secured within a glass pinch 17. Surrounding the cathode structure is acontrol grid/screen grid structure 18, which conveniently may be referred to as a double grid, which is shown in greater detail in FIGS. 1 and 2. The inner rods of the double grid 13 pass through suit ably shaped apertures in mica discs 14 and metal shield plates 14a to locate the double grid 18 correctly in spaced relationship with cathode tube 169. Anode plates 19 are located on either side of the double grid 13 and spaced from the screen grid helix '7. The anode plates 19 have lugs 21? which pass through the mica discs 14 and shield plates 14a to hold the anode plates 19 in position.

Filament supply wires 21 support the assembly so far escribed from the glass pinch 17 and the portions of the wires 21 extending between the mica discs'14- are enclosed by ceramic tubes 22. These tubes 22 prevent wires 21 acting as auxiliary anodes when the filament is supplied from a voltage source of comparable potential to the plate supply of anodes 19. The wires 21 are connected to the respective ends of filament wire 11 by clips 23.

Connections to the cathode 19 are made via a lead 24 connected to wire 25 carried by the glass pinch 17. The glass pinch also supports wire 26 connected to a Y-shaped connector 27 (only one arm being shown in FIG. 3) which is secured to the lower lugs 2t) of anodes 19; wire 28 carried by the glass pinch is connected to the screen grid helix 7 by means of the platinum tape 3. A clip 29 is welded to the upper end of one of the metal inner rods 1, around which the control grid helix is wound, and carries a connecting wire Ell. The shield plates 14a are connected together by rods 14b (shown only in FIG. 4) one of which is connected to a wire 25a carried by the glass pinch 1'7.

The above assemblage of electrodes, mica discs 14 and shield plates 1 1a supported on the glass pinch 17 by leads 21, is housed within a precision bore glass envelope 31, the mica discs 14 being so shaped 'and dimensioned as to locate the electrode structure accurately within the envelope 31 which at its lower end is sealed to the glass pinch 1'7 in the usual manner. Leads are taken from respective wires 21, 25, 25a, 26 and 28 to pins in a base member secured to the lower end of the pinch 1'7 and envelope 31 as is well-known in the art; the control grid lead 31) passes through the top of the envelope which is sealed to this lead, the projecting lead being secured to the usual metal top cap (not shown).

The electrode structure of the valve described may be assembled in the following manner. The double grid 13 is supported between spaced arms of a movable jig. The cathode tube 10 is inserted in the central aperture of the lower mica disc 14 sandwiched between shield plate 14a and accurately positioned between the spaced arms of the jig so that when these arms are lowered the cathode tube 111! is symmetrically located within the control grid helix 4 and the rods 1 are received by their co-operating apertures in mica disc 14. The other mica disc 14 is then positioned at the upper end of the structure to receive and locate the double grid and the cathode. Anode plates 19 are then placed in position by passing their lugs 2th through co-operating apertures in mica discs 14. The filament 11, mounted in its insulating tube 13, is then inserted in cathode tube 10. The completed structure is a screen grid potential .of 40 volts" mutual conductances of greater than 20 ma./volt have beenmeasured at an anode current of 15 ma. the. grid base being adequate for a peak anode current of twice the static value.

Variations of the grid structure as described with reference to FIGS. 1 arid 2 may also be employed.

For example, the rods on which the control grid helix is wound may be made of a refractory insulating material as well as the rods supporting the screen grid helix. Both sets of rods are then secured to metal end plates. Such a construction is shown in FIGS. 6 and 7.

The grid helix supporting rods 1' and 5 are supported between rectangular metal end'plates 40 which conveniently maybe made of molybdenum. Each plate 40 has a central rectangular aperture 41 for accommodating a cathode/heater assembly. Arranged symmetrically on either side of aperture 41 are apertures 42, 43, 44 and 45. Apertures 42, 43 and 44 are generally D-shaped whilst aperture 45 iscircular. Apertures 44 and 45 are of larger size than apertures 42 and 43 in order to accommodate the larger diameter rods 5. Further, apertures 42 and 45 have keyway-like slots 46 and 47 respectively the purpose of which will be explained hereinafter. The shapes of rods 1 and 5 are modified from the shapes shown in FIGS. 1 and: 2 in that they have flats formed at either end to give the end portions of the respective rods D- shaped sections which co-operate with their associated apertures 42 43, 44-or 45.

The grid structure shown in FIGS G and 7 is assembled in the following manner. The respective ends of a rod 1 are located in aperture 42 of upper plate 40 and aperture 43 of the lower plate 40. The other rod1 is similarly located with its respective ends passing through aperture 43 of the upper plate and aperture 42 of the lower plate. The plates 40 are arranged so that the shoulders formed by the flats on rods 1 abut plates 40. The rods 1 and plates 40 are then cemented together to form a rigid frame and the control grid helix 4 (not shown) is then wound under tension around the rods 1 in the manner described with reference to FIGS. 1 and 2.

One end of a rod 5 is then inserted through aperture 45 of the upper plate 40 and passed through aperture 44 of the lower plate 40 so that the shoulder formed by the fiat on that end of rod 5 abuts the lower plate. That rod 5 is then cemented in position. One end of the other rod 5 is then passed through aperture 45 of the lower plate 40 to engage with aperture 44 of the upper plate in a similar manner and is then cemented in position. Screen grid helix 7 is then wound under tension around the rods 5 as previously described.

Connections to the helices 4 and 7 are made by entrapping a platinum tape (not shown) between the windings of the helices and a rod 1 or 5 respectively, the respec tive tapes passing through either slot 46 or 47 in clearance with plates 40.

The helices 4 and 7 are cemented and fired as described with reference to FIGS. 1 and 2.

Alternatively, both pairs of rods 1 and 5 may be made of metal and passed through insulating bushes, for example made of synthetic ruby, which are rigidly set in metal end plates as is horological practice. Such a construction is shown in FIGS. 8 and 9.

Rectangular molybdenum end plates 55 each has a central rectangular aperture 51 for accommodating a cathode/heater assembly. The plates 50 support rods 1 I bushes 54. a

A grid structure as shown in FIGS. 8 and. 9 is assembled as follows:

Rods 1 are passed through respective apertures 52 and upper and lower plates 50, the rods being dimensioned to fit closely within the bushes 54, and fixed in position so that rods 1 and plates 50 form a rigid frame. A control grid helix 4 is then wound around rods 1 in the manner described with refernce to FIGS. 1 and 2. Screen grid rods 5 of greater diameter than rods 1 are then inserted in-respective apertures 53 of upper and lower plates 50, rods5 conforming closely to the internal bore of bushes 55. A screen grid helix '7 is then wound around rods 5 as described with reference toFIGS. 1 and 2. cementing of the helices 4 and '7 and firing of the assembly is also carried out in a similarmanner to that previously described.

The grid structures as described with reference to F168. 6 and 7 andFIGS. 8 and 9 respectively when assembled have suitably apertured mica discs positioned over the portion of rods 1 and 5 which project through the respective upper and lower plates 40 and 50. These mica discs are shaped and dimensioned to position accurately complete electrode structure, assembled in a manner similar to that described with reference to FIGS.

3, 4 and 5, in a precision bore tubular glass envelope.

I claim: 1. A unitary frame grid structure for an electronic valve comprising in combination:

(a) a frame having in planarjparallel alignment two inner control grid support rods and two outer screen grid support rods, andplural common bracing members located adjacent to respective ends of the control and screen grid rods to space and support said control grid rods in planar parallel alignment with each other as well as in planar parallel alignment with said outer screen grid support rods,

(1)) a control grid helix stretched around said inner rods under a tension suflicient to maintain said helix on said inner rods,

(c) a screen grid helix stretched around said outer rods under a tension sufficient to maintain said helix on said outer rods,

(d) the said bracing members extending transversely of and engaging solely with the sides of the control and screen grid rods to maintain the control grid rods in the said planar parallel alignment with each other and with the screen grid rods, and to rigidly brace the said control and screen grid rodsagainst the loading imposed on them by the said tensioned control and screen grid helices, and

(e) the structure so intervening between the said control grid and screen grid helices comprising insulating material for electrically insulating the said grid helices from each other.

2. An electronic valve grid structure according to claim 1, in which the inner rods and bracing members are made of an electrically conductive metal and the outer rods of a refractory insulating material.

3. An electronic valve grid structure according to claim 1, in which the inner rods and bracing members are made of molybdenum and the outer rods are made of synthetic sapphire.

4. A method of manufacturing a unitary plural grid structure for an electronic valve which comprises, in combination, the steps of:

(a) forming a tensioning frame comprising two inner control grid supporting rods and spacing means engaging and rigidly maintaining the same in spaced parallel relation to each other,

(b) winding a control grid helix around the said inner rods under a tension sutficient to maintain said helix in position on said inner rods to thus form a first sub-assembly,

(c) thereafter assembling to said sub-assembly in parallel relation to said inner rods two screen grid support rods positioned adjacent to and outwardly of said inner rods to form a second sub-assembly,

(d) thereafter winding a screen grid helix around the said outer rods of said second sub-assembly in surrounding spaced relation to said control grid helix under a tension sufficient to maintain said helix in position on said outer rods, and

(e) effecting insulation of said screen grid helix from said control grid helix by interposing insulating material therebetween during at least one of said steps (a) through (d).

5. Method as defined in claim 4, in which electrically conductive spacing means is employed in step (a) and in which said step (e) is practiced by employing grid support rods of insulating material in at least one of said steps (a) and (c).

6 Method as claimed in claim 4, in which electrically conductive spacing means is employed in step (a), in which electrically conductive sets of grid support rods are employed in steps a and (c) and in which said step (e) is practiced by providing insulation between said spacing means and at least one of said sets of support rods in at least one of steps (a) and (c).

7. Apparatus as claimed in claim 1, wherein said bracing members are electrically conductive and at least one of the sets respectively comprising said inner control grid support rods and said outer screen grid support rods is formed of insulating material.

8. Apparatus as claimed in claim 1, wherein the sets comprising said inner and outer grid support rods are conductive and wherein said bracing members are compositely constructed, each comprising conductive material having insulating inserts engaging with at least one of the said sets.

9. Apparatus as claimed in claim 7, in which said conductivebracing members consists of metallic plates of greater area than the cross-section of said screen grid helix both mechanically supporting said supportrods and electrically shielding the ends of said control and screen grid helices.

10. Apparatus as claimed in claim 1, wherein said inner control grid support rods and said bracing members are electrically conductive, and said bracing members comprise two pairs of cross-straps physically bonded to the inner control grid rods and engaging the outer screen grid rods, the cross-straps of each pair being located opposite each other on either side of the rods.

11. Apparatus according to claim 10, in which the inner control grid support rods and the said cross-straps are made of molybdenum and are brazed together by a brazing alloy consisting of 75% gold and 25% nickel.

12. A 'tetrode electronic valve including a cathode/ heater assembly, an anode structure, and a unitary control-screen grid structure comprising a frame having in planar parallel alignment two inner control. grid support rods and two outer screen grid support rods and common spacing means engaging and rigidly supporting said rods in such alignment; a control grid helix stretcher around said inner rods under a tension sufiicient to maintain said helix on said inner rods; and a screen grid helix stretched around said outer rods under a tension sufiicient to maintain said helix on said outer rods; the structure so intervening between said control grid and screen grid helices comprising insulating material for electrically insulating said grid helices from each other, the cathode/heater assembly being located Within the control grid helix and the anode structure arranged outwardly and spaced apart from the screen grid helix.

References Cited by the Examiner UNITED STATES PATENTS V 2,945,152 7/60 Marx 313 350 3,114,071 Weber et a1.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner. V 

1. A UNITARY FRAME GRID STRUCTURE FOR AN ELECTRICAL VALVE COMPRISING IN COMBINATION: (A) A FRAME HAVING A PLANAR PARALLEL ALIGNMENT TWO INNER CONTROL GRID SUPPORT RODS AND TWO OUTER SCREEN GRID SUPPORTS RODS, AND PLURAL COMMON BRACING MEMBERS LOCATED ADJACENT TO RESPECTIVE ENDS OF THE CONTROL AND SCREEN GRID RODS TO SPACE AND SUPPORT SAID CONTROL GRID RODS IN PLANAR PARALLEL ALIGNMENT WITH EACH OTHER AS WELL AS IN PLANAR PARALLEL ALIGNMENT WITH SAID OUTER SCREEN GRID SUPPORT RODS, (B) A CONTROL GRID HELIX STRETCHED AROUND SAID INNER RODS UNDER A TENSION SUFFICIENT TO MAINTAIN SAID HELIX ON SAID INNER RODS, (C) A SCREEN GRID HELIX STRETCHED AROUND SAID OUTER RODS UNDER A TENSION SUFFICIENT TO MAINTAIN SAID HELIX SAID OUTER RODS, (D) THE SAID BRACING MEMBERS EXTENDING TRANSVERSELY OF SAID ENGAGING SOLELY WITH THE SIDES OF THE CONTROL AND SCREEN GRID RODS TO MAINTAIN THE CONTROL GRID RODS IN THE SAID PLANAR PARALLEL ALIGNMENT WITH EACH OTHER AND WITH THE SCREEN GRID RODS, AND TO RIGIDLY BRACE THE SAID CONTROL AND SCREEN GRID RODS AGAINST THE LOADING IMPOSED ON THEM BY THE SAID TENSIONED CONTROL AND SCREEN GRID HELICES, AND (E) THE STRUCTURE SO INTERVENING BETWEEN THE SAID CONTROL GRID AND SCREEN GRID HELICES COMPRISING INSULATING MATERIAL FOR ELECTRICALLY INSULATING THE SAID GRID HELICES FROM EACH OTHER. 